1. Field of the Invention
The present invention generally relates to a piston type refrigerant compressor and, more particularly, to a slant plate type compressor, such as a swash or wobble plate type compressor, with a variable displacement mechanism suitable for use in an automotive air conditioning system.
2. Description of the Prior Art
A swash plate type refrigerant compressor with a variable displacement mechanism suitable for use in an automotive air condition system is disclosed in U.S. Pat. No. 4,789,311.
In a swash plate type compressor, the pistons reciprocate in cylinder bores and in response to the movement of a swash plate. The swash plate is fixedly secured to a drive shaft in such a manner as to be slanted with respect to the drive shaft. The pistons are coupled to the swash plate through bearing means comprising shoes. Referring to FIG. 9, a plurality of cylinder bores 87 are arranged in parallel with each other within cylinder block 3. Drive shaft 12 is arranged coaxially with the annular arrangement of cylinder bores 87. Pistons 67 are reciprocatingly inserted into cylinder bores 87. Pistons 67 are formed such that the middle portion of each piston 67, i.e., coupling portion 67a, is operatively connected with both sides of peripheral portion of swash plate 18 through shoes. Coupling portion 67a has a substantially semicircular cross-section, and two piston heads are coupled together through coupling portion 67a. Supporting portion 67b which is formed inside of coupling portion 67a supports the shoes. Cross-sections of cylinder bores 87 cut perpendicular to the longitudinal axis of drive shaft 12 are circular in shape. A clearance exists between the radial end extremity of swash plate 18 and each piston 67 because such swash plate type compressors with variable displacement typically require a relatively large clearance in order to vary the capacity of compression by changing the piston stroke.
In this configuration, the relatively large clearance allows pistons 67 to rotate within cylinder bores 87 and create noise due to collisions between the inner surface 67c of each piston 67 and the radial end extremity of the swash plate 18. As a result, an expensive wear resistant coating must be applied to prevent wear of inner surface 67c. Further, each piston 67 must be provided with a rotation prevention mechanism to prevent the noise described above. As a result, the structure of the compressor becomes more complex, and the manufacturing process of such compressors becomes more complicated. Because of this complex structure and the complicated manufacturing process, the associated manufacturing cost increases greatly, and the productivity of manufacturing facilities declines.